Epidemiology and Virulence Profiling of Colletotrichum spp. Causing Turmeric Leaf Spot in Kerala, India

Abstract

Turmeric, Curcuma longa L., is an economically important spice crop that is increasingly threatened by leaf spot disease caused by species of Colletotrichum genus. An epidemiological survey was conducted across major turmeric-growing regions in Kerala, India, covering the districts of Thiruvananthapuram, Kollam, and Palakkad. High disease pressure was recorded across all surveyed locations, with the Percent Disease Index (PDI) reaching a critical maximum of 64.07% in the Vellanad region (Thiruvananthapuram). A total of twelve fungal isolates were obtained and characterized based on morphological, cultural, and pathogenic features. Among them, isolate CT3, collected from the highly diseased region, displayed significantly higher virulence, evidenced by its shortest duration for symptom appearance (6.33 days) and the largest necrotic lesion area (12.92 cm2). Molecular characterization of CT3 through 28S rRNA sequencing confirmed the isolate as Colletotrichum gloeosporioides (PX369133). This study verifies the presence of highly virulent strains of C. gloeosporioides associated with severe leaf spot epidemics in Kerala, and provides essential insights to support the development of Integrated Disease Management (IDM) strategies, particularly in guiding fungicide application schedules, screening for resistant cultivars, and designing region-specific management interventions.